WO2005108068A1

WO2005108068A1 - Heat-shrinkable multilayer films

Info

Publication number: WO2005108068A1
Application number: PCT/EP2005/004174
Authority: WO
Inventors: Walter Bernig; Christoph Schweitzer
Original assignee: Cfs Kempten Gmbh
Priority date: 2004-05-06
Filing date: 2005-04-19
Publication date: 2005-11-17
Also published as: AU2005240288A1; US20070298198A1; US7722936B2; DE502005008626D1; RU2401202C2; AU2005240288B2; ATE450371T1; DE102004023023A1; EP1744879B1; EP1744879A1; RU2006142892A; NZ550895A; CA2565631A1

Abstract

The invention relates to heat-shrinkable multilayer films comprising a surface layer that is based on at least one olefinic polymer and/or copolymer, a layer based on a mixture of an ionomer having a maximum MFI of 4dg/min and an ionomer having an MFI > 4dg/min, a barrier layer based on polyvinylidene chloride or a vinylidene chloride polymer, a layer based on said ionomer mixture or an olefinic copolymer, and a sealing layer which is composed of at least one polyolefin or olefinic copolymer, preferably as tubular film. Also disclosed are the use thereof as a packaging and the corresponding tubular film packagings.

Description

Heat shrinkable multilayer films

The present invention relates to heat-shrinkable multilayer films comprising a surface layer based on at least one olefinic polymer and / or copolymer, a layer based on a mixture of an ionomer with an MFI of up to 4dg / min and an ionomer with an MFI> 4dg / min, a barrier layer based on polyvinylidene chloride or a vinylidene chloride copolymer, a layer based on said ionomer mixture or an olefinic copolymer and a sealing layer of at least one polyolefin or olefinic copolymer, preferably as a tubular bag, its use as packaging or the corresponding tubular bag packaging.

Biaxially oriented, heat-shrinkable multilayer films are used in the packaging of foods, in particular perishable foods such as poultry or fresh meat, these multilayer films preferably having an oxygen barrier layer. Heat-shrinkable multilayer films have the property of shrinking back to their original, unoriented dimensions when heated to their softening point. Biaxially oriented multilayer films are stretched both in the longitudinal and in the transverse direction according to their manufacturing process and preferably have at least a shrinkage of 35% in the longitudinal or machine direction as well as in the transverse direction, i. H. against the machine direction.

Already commercially used, biaxially oriented, heat-shrinkable multilayer films preferably have an outer layer made of an ethylene / vinyl acetate copolymer optionally mixed with a polyethylene, preferably an LLDPE, and as an oxygen barrier layer a layer based on polyvinylidene chloride, since these thermoplastic materials have excellent shrinkage behavior.

A disadvantage of such multilayer films is their possibly insufficient strength, ie insufficient puncture resistance when the shrink film is subjected to mechanical stress, such as, for. B. when packaging food with outstanding Bone. In order to improve the puncture resistance, heat-shrinkable multilayer films have already been equipped with an ionomer layer based on an ethylene / acrylic acid copolymer, which is partly in the form of the sodium salt. However, in order to achieve adequate bond between such an ionomer layer and a barrier layer based on polyvinylidene chloride, it was necessary to insert a conventional adhesion promoter layer. This measure means not only higher material and manufacturing costs for such shrinkable multilayer films, but also greater thicknesses, which is rather undesirable in heat-shrinkable multilayer films. In addition, more complex extrusion devices are necessary.

It was therefore an object of the present invention to provide a heat-shrinkable multilayer film which has improved mechanical strength, in particular higher puncture resistance and at the same time sufficient bond adhesion without the use of an adhesion promoter layer between the strength-enhancing ionomer layer and the barrier layer and thus thinner than a corresponding one is multilayer film used commercially.

The object is achieved by providing the heat-shrinkable, biaxially oriented multilayer film according to the invention, which comprises the following layer structure: a) a surface layer based on at least one olefinic polymer and / or copolymer, b) a layer based on a mixture of an ionomer with an MFI up to a maximum of 4 dg / min and an ionomer with an MFI> 4dg / min, c) a barrier layer based on polyvinylidene chloride or a vinylidene chloride copolymer d) a layer based on the ionomer mixture according to layer b) or a conventional adhesion promoter based on an olefinic copolymer e) a sealing layer of at least one polyolefin or olefinic copolymer.

Layer a), which is usually used in the multilayer film according to the invention as the outer layer of a packaging, such as, for. B. a shrink bag, is preferably based on a polyethylene (PE), particularly preferably on a PE with a density <0.92 g / cm ³ or m-PE (metallocene polyethylene) and / or an ethylene copolymer, particularly preferably an ethylene / vinyl acetate copolymer. Layer a) is very particularly preferably based on a mixture of an LLDPE (linear low-density polyethylene) or m-PE and an ethylene / vinyl acetate copolymer, the mixture preferably consisting of 70 to 90% by weight of LLDPE and / or m-PE , 10 to 30% by weight of ethylene / vinyl acetate copolymer and optionally up to 5% by weight of conventional additives, in each case based on the total weight of layer a) at 100% by weight.

Common additives are understood to be anti-blocking agents, antistatic agents and / or lubricants.

The thickness of layer a) is preferably less than 20% of the total thickness of the heat-shrinkable multilayer film according to the invention. The thickness of this layer is particularly preferably in the range from 5 to 10 μm.

Layer b), which adjoins the outer layer a) and is connected to the barrier layer c), is based on a mixture of ionomers, ie a mixture of ethylene / acrylic acid copolymers or ethylene / methacrylic acid copolymers, each of which is at least partially, preferably up to 35%, as salt, preferably as Na or Zn salt, a mixture component preferably having an MFI of 1.5 to 4 dg / min, particularly preferably up to a maximum of 2dg / min, and the second mixture component an MFI to has a maximum of 5dg / min. The two mixture components are present in the mixture in an amount of 35 to 65% by weight or 65 to 35% by weight, in each case based on the total weight of layer b) at 100% by weight. The mixture should very particularly preferably have an MFI in the range from 1.5 to 4 dg / min.

The melt index (MFI) is always determined according to ASTM 1238 (at 190 ° C 2.16 kg / 10 min).

The thickness of layer b) is preferably in the range from 5 to 10 μm, very particularly preferably in the range from 6 to 8 μm.

The barrier layer c) is based on a polyvinylidene chloride or a vinylidene chloride / methacrylic acid copolymer with up to 10% by weight of methacrylic acid units.

Layer c) preferably has a thickness of 3 to 8 μm, very particularly a thickness of 4 to 6 μm.

It gives the heat-shrinkable multilayer film according to the invention an oxygen permeability of at most 20 cc / m ² .d.bar, preferably in the range from 7 to 15 cc / m ² .d.bar.

Layer d) is preferably based on an olefinic copolymer, particularly preferably on an ethylene copolymer, very particularly preferably on an ethylene / vinyl acetate copolymer, which can further increase the strength of the film according to the invention.

For production reasons, however, it is also possible to produce layer d) from the same ionomer mixture as layer b).

Layer d) preferably has a thickness of 5 to 10 μm, particularly preferably a thickness in the range of 6 to 9 μm.

If an ethylene / vinyl acetate copolymer is present in the outer layer a) or in layer d), this copolymer consists of preferably 10 to 30 mol%, particularly preferably 12 to 20 mol%, of vinyl acetate units. Layer e), which serves as a sealing layer and, in a packaging made of the multilayer film according to the invention, represents the layer facing the filling, is based on at least one polyolefin or olefinic copolymer, preferably at least one polyethylene, particularly preferably on a mixture of m-PE (metallocene polyethylene ), particularly preferably with a density equal to or greater than 0.9 g / cm ³ , and an LLDPE with a density equal to or greater than 0.9 g / cm ³ . The mixture preferably contains 70 to 85% by weight of m-PE, 30 to 15% by weight of LLDPE and possibly up to 5% by weight of conventional additives, in each case based on the total weight of layer e) at 100% by weight. Layer e) can also be based on at least one polypropylene and / or propylene copolymer, preferably a propylene / ethylene copolymer.

Anti-blocking agents, antistatic agents and / or lubricants are preferably used as additives.

The thickness of the sealing layer is at least 25%, preferably up to 35% of the total thickness of the multilayer film according to the invention. The thickness is particularly preferably at least 10 μm, very particularly preferably in the range from 10 to 20 μm.

The thickness information is understood as the thickness of the respective layer of the multilayer film according to the invention after the longitudinal and transverse orientation.

The multilayer film according to the invention is preferably after the film blowing process by co-extrusion such. B. described in US-A-3,456,044. However, it is also possible first to extrude only layer a) as a tube and to apply the subsequent layers by means of a co-extrusion, or to first extrude any sub-layer combination as a tubular film and then immediately connect it to the remaining layers by extrusion. Furthermore, it is possible to produce the multilayer film according to the invention using the chill roll method with longitudinal and transverse orientation.

During manufacture, the film is preferably in the machine direction, i.e. H. lengthways in a ratio of 1: 3 to 1: 5, particularly preferably from 1: 3.5 to 1: 4.5 and transversely to the machine direction, in a ratio of 1: 3 to 1: 5, particularly preferably 1: 3, 5 to 1: 4.5, oriented.

In the multilayer film according to the invention, one or all layers of the multilayer film according to the invention can be crosslinked in order to improve their wear and / or puncture resistance. This crosslinking can be achieved using β-radiation (high-energy electrons) and the like. The radiation source can be any electron beam generator that operates in a range from about 150 kV to about 300 kV. The irradiation is usually carried out at a dose of up to 60 kGy, a preferred dose being in the range from 30 kGy to 50 kGy. As already mentioned, such radiation can be applied to the entire film or to individual layers such as e.g. B. the outer layer can be limited.

The polymers used for the layer structure are commercial products and have been adequately described in the prior art. To produce the multilayer films according to the invention, they are usually mixed as necessary in conventional mixing apparatus as pellets or granules and are brought into the desired final shape by melting, preferably with the aid of extruders. As already mentioned, production by the film blowing method is preferred, extruders with co-extruder nozzles being used as extruders, which ensure the formation of a tube. The processing temperatures, in particular in the case of extrusion, are known to the person skilled in the art and are generally indicated when the plastics are made available.

The multilayer films according to the invention are outstandingly suitable as packaging material, in particular as shrinkable shrink bags with excellent optical and mechanical properties. Another object of the invention is the use of the invention Multi-layer films for packaging all kinds of goods, preferably food, packaging made from them; preferably tubular bag packaging.

Method for testing the bond adhesion after shrinking the film

Tools required

Material to be tested (multi-layer film) block according to the invention (size WxHxD = 150 mm x 120 mm x 30 mm) foil knife razor blade immersion bath with a water temperature of 93 ° C. ethanol IR spectrometer

execution

An approximately 130 mm long piece is cut off from the multilayer film tube according to the invention to be tested and the tube is slit open at a folding seam. The longer narrow side of the block is placed on the remaining folded seam of the hose so that the two sides of the film enclose the block from the outside and the ends of the film are held over the block. The film must not protrude beyond the corners of the block.

The shrinkage of the film is carried out by immersing the block with film for 6 seconds in 93 ° C (± 1 ° C) hot water. Six samples of the multilayer film are shrunk. 15 mm wide film test strips (at right angles to the machine direction) are cut out in the most wrinkle-free areas, which lie in the shrunk area. 6 test strips are required. At the test site, the film is scratched with the help of a razor blade and the composite is dissolved with ethanol, thus preparing six test strips with a separation between layer b) and layer c). The separation is checked using an IR spectrometer. The six test strips are then tested for bond strength (bonded adhesion) at the separation point using the UTS 2 universal tensile testing machine (software program composite adhesion in accordance with DIN 53357). The trigger angle is 90 ° in each case. The result is recorded electronically. The measured value of the bond adhesion is given in N / 15 mm. Method of testing shrinkability

To measure the shrinkability of a film according to the invention, a crosshair 10 x 10 cm is recorded on the film sample to be tested with a film pen, with a bar in the machine direction (md), i.e. H. Direction of extrusion and the second bar of the crosshair is drawn transversely to the machine direction (cma). The water bath in which the film sample is immersed for 6 seconds has a temperature of 93 ° C.

After 6 seconds, the sample is removed and indicated by measuring the shortening of the crosshairs for the respective direction in%.

Examples

example 1

A multilayer film according to the invention with the following layer structure: a) a surface layer made of 81% by weight LLDPE with a density of 0.911 g / cm ³ , 15% by weight of an ethylene / vinyl acetate copolymer with 28 mol% vinyl acetate and 4% by weight of an antiblocking agent and a thickness of 8 microns b) a layer of a mixture of 50 wt.% of ionomer (Surlyn ^® from Du Pont) having an MFI of 1, 3 dg / min and 50 wt.% of an ionomer (Surlyn ^® from Du Pont) with an MFI of 4.3 dg / min, each of which was 35% Na salt, and a thickness of 7 μm c) with a barrier layer based on polyvinylidene chloride (Ixan PVS from Solvin GmbH & Co. KG) a thickness of 5 μm d) a layer of the ethylene / ethyl acetate copolymer which is identical to the copolymer in layer a), a thickness of 8 μm and e) a sealing layer of a mixture of 73% by weight of polyethylene with a Density of 0.895 g / cm ³ , 24% by weight of an LLDPE with a density of 0.911 g / cm ³ and 3 G % of an antiblocking agent and with a thickness of 15 μm; was produced using a blown film coextrusion process with an orientation of 1: 4 both in the machine direction and in the transverse direction. The multilayer film was crosslinked using electron radiation at 190 kV with a dose of 50 kGy.

The shrinkability was measured according to the above method and was approximately 40%.

The measurement of the bond adhesion, measured according to the method given above, was 2.0 N / 15 mm.

Comparative Example 1

As indicated in Example 1, a multilayer film with an identical structure was produced with the exception of layer b). Layer b) was prepared from an ionomer (Surlyn ^®) having an MFI of 1, 0 dg / min prepared. The respective layer thicknesses, the orientation and crosslinking corresponded to the multilayer film according to Example 1.

The shrinkability was determined by the method given above and was approximately 40%.

The bond adhesion measured by the method given above was only 0.121 N / 15 mm.

Claims

claims

1. Biaxially oriented, heat-shrinkable multilayer film comprising the following layer structure: a) a surface layer based on at least one olefinic polymer and / or copolymer, b) a layer based on a mixture of an ionomer with an MFI of up to 4 dg / min and an ionomer with an MFI> 4dg / min, c) a barrier layer based on polyvinylidene chloride or a vinylidene chloride copolymer d) a layer based on an ionomer mixture according to layer b) or an olefinic copolymer, e) a sealing layer based on at least one polyolefin and / or olefinic copolymers ,

2. Multi-layer film according to claim 1, characterized in that the layer a) as an olefinic polymer is a polyethylene, preferably a polyethylene with a density <0.92 g / cm ³ or m-PE, and / or as an olefinic copolymer, an ethylene copolymer, preferably an ethylene / vinyl acetate copolymer.

3. Multi-layer film according to claim 1 or 2, characterized in that layer a) is based on a mixture of LLDPE and / or m-PE and ethylene / vinyl acetate copolymer.

4. multilayer film according to claim 3, characterized in that the mixture of 70 to 90 wt.% LLDPE and / or m-PE, 10 to 30 wt.% Ethylene / inyl acetate copolymer and optionally up to 5 wt.% Of conventional additives , based in each case on the total weight of layer a) at 100% by weight.

5. Multi-layer film according to one of claims 1 to 4, characterized in that the layer a) has a thickness which is less than 20% of the total thickness of the multi-layer film.

6. Multi-layer film according to one of claims 1 to 5, characterized in that the layer b) contains ionomeric ethylene / acrylic acid copolymers or ethylene / methacrylic acid copolymers, each of which is at least partially present as sodium or Zn salt.

7. Multi-layer film according to one of claims 1 to 6, characterized in that one ionomer has an MFI of up to 2dg / min and the second ionomer has an MFI of up to 5 dg / min.

8. Multi-layer film according to one of claims 1 to 7, characterized in that the mixture of layer b) consists of 35 to 65% by weight of one ionomer and 65 to 35% by weight of the second ionomer.

9. Multi-layer film according to one of claims 1 to 8, characterized in that the layer b) has a thickness of 5 to 10 microns.

10. Multi-layer film according to one of claims 1 to 9, characterized in that layer c) is based on a polyvinylidene chloride or a vinylidene chloride / methacrylic acid copolymer.

11. Multi-layer film according to one of claims 1 to 10, characterized in that the layer c) has a thickness of 3 to 8 microns.

12. Multi-layer film according to one of claims 1 to 11, characterized in that layer d) is based on an ionomer mixture corresponding to the ionomer mixture of layer b) or on an ethylene copolymer, preferably an ethylene / ethyl acetate copolymer.

13. Multi-layer film according to one of claims 1 to 12, characterized in that the thickness of layer d) is 5 to 10 microns.

14. Multi-layer film according to claim 3 or 12, characterized in that the ethylene / vinyl acetate copolymer has up to a maximum of 30 mol% of vinyl acetate units.

15. Multi-layer film according to one of claims 1 to 14, characterized in that layer e) is based on at least one polyethylene, preferably on a mixture of polyethylenes, on at least one polypropylene or propylene copolymers, preferably propylene / ethylene copolymers.

16. Multi-layer film according to claim 15, characterized in that layer e) is based on a mixture of m-PE and LLDPE.

17. Multi-layer film according to one of claims 1 to 16, characterized in that the polyethylene mixture of layer e) consists of 70-85% by weight of m-PE and 30-15% by weight of LLDPE and optionally up to 5% by weight of conventional additives , each based on the total weight of layer e) with 100% by weight.

18. Multi-layer film according to one of claims 1 to 17, characterized in that the thickness of layer e) makes up at least 25%, preferably up to 30% of the total thickness of the multi-layer film.

19. Multi-layer film according to one of claims 1 to 18, characterized in that the layer e) has a thickness of at least 10 microns, preferably from 12 to 20 microns.

20. Multi-layer film according to one of claims 1 to 19, characterized in that the multi-layer film has a stretch ratio in the longitudinal direction of 1: 5 to 1: 3 and in the transverse direction of 1: 5 to 1: 3.

21. Multi-layer film according to one of claims 1 to 20, characterized in that the multi-layer film is a tubular film.

22. Use of a multilayer film according to one of claims 1 to 21 for the production of a tubular bag.

23. tubular bag made of a film according to one of claims 1 to 21.

24. A tubular bag according to claim 23 for packaging a wide variety of goods, preferably food.

25. Packaging from a tubular bag according to claim 23 or 24.